The present invention relates generally to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device having a diffusion barrier with improved characteristics thereby improving the characteristics of a metal line, and a method for forming the same.
In a typical semiconductor device, metal lines are formed to electrically connect elements or lines to each other, and contact plugs are formed to connect lower metal lines to upper metal lines. In order to conform to the trend towards high integration in semiconductor devices, the design rule of a semiconductor device has decreased. When the design rule is decreased, the aspect ratio of a contact hole in which a contact plug is to be formed is increased. The increase in the aspect ratio of a contact hole leads to difficulty in forming the metal line and the contact plug, and thus the importance of the metal line an contact plug forming processes has been noted.
Aluminum and tungsten have wide use as a material for forming the metal line of a semiconductor device due to the good electrical conductivity of these materials. Recent undertakings have explored the potential of copper as a next-generation material for a metal line due to the excellent electrical conductivity and the low resistance of copper when compared to aluminum and tungsten. Copper (Cu) can therefore solve the problems associated with RC (resistance-capacitance) signal delay in a semiconductor device having a high level of integration and high operating speed.
However, unlike aluminum, when copper is used as the material for a metal line, copper diffuses through an insulation layer to the semiconductor substrate. Semiconductor substrates are typically made of silicon, and the diffused copper acts as a deep-level impurity and induces leakage current. Therefore, it is necessary to form a diffusion barrier at the interface between a copper layer for a metal line and the insulation layer.
Hereinbelow, a conventional method for forming a metal line of a semiconductor device will be briefly described.
After forming an insulation layer on a semiconductor substrate, a metal line forming region is defined by etching the insulation layer. Then, a diffusion barrier is formed on the insulation layer including on the surface of the metal line forming region, and a copper seed layer is formed on the diffusion barrier. Next, a copper layer is formed on the copper seed layer, and the copper layer is chemically and mechanically polished (CMP) to form a metal line comprising the copper layer.
However, in the conventional method described above, as the size of cells decreases in conformance with the trend toward high integration of a semiconductor device, it becomes difficult to properly prevent the diffusion of a copper constituent by means of the diffusion barrier formed according to the conventional method.
Also, in the conventional method described above, it is difficult to increase the thickness of the diffusion barrier so as to improve the characteristics of the diffusion barrier. Due to this fact, the characteristics of the diffusion barrier become worse, and thereby the resistance of the metal line increases. As a consequence, the characteristics and the reliability of the semiconductor device along with the characteristics of a metal line are likely to be diminished.